CN118164764A

CN118164764A - Preparation method of pressureless sintered silicon carbide gel injection molding

Info

Publication number: CN118164764A
Application number: CN202410280809.8A
Authority: CN
Inventors: 方仁德; 王震; 闫永杰
Original assignee: Nantong Sanze Precision Ceramics Co ltd; Jiangsu Sanwei New Materials Technology Co ltd
Current assignee: Nantong Sanze Precision Ceramics Co ltd; Jiangsu Sanwei New Materials Technology Co ltd
Priority date: 2024-03-12
Filing date: 2024-03-12
Publication date: 2024-06-11

Abstract

The application relates to a preparation method of pressureless sintered silicon carbide gel injection molding, which comprises the following steps: mixing and dispersing modified silicon carbide ultrafine powder, a monomer and a crosslinking agent into water, stirring, adding an initiator, carbon black and a dispersing agent, uniformly mixing, and then removing bubbles in vacuum to obtain mixed slurry; adding the mixed slurry into a mold, immersing the bottom of the mold filled with the mixed slurry into a freezing bath, demolding after the reaction is completed to obtain a wet blank, drying the wet blank to obtain a dry blank, and performing pressureless sintering on the dry blank to obtain the silicon carbide ceramic. The application has the effect of improving the drying performance of the pressureless sintered gel injection molding silicon carbide.

Description

Preparation method of pressureless sintered silicon carbide gel injection molding

Technical Field

The application relates to the technical field of silicon carbide ceramics, in particular to a preparation method for pressureless sintering silicon carbide gel injection molding.

Background

The silicon carbide ceramic material has excellent physicochemical properties, and has the characteristics of high hardness, small thermal expansion coefficient, high thermal conductivity, good semiconductor performance and the like. Therefore, silicon carbide ceramics are widely used in the fields of manufacturing high-temperature resistant materials, wear-resistant materials, semiconductors and the like.

In recent years, new colloidal molding such as press molding, gel casting, direct solidification casting, and the like is an effective method for producing highly reliable, complex-shaped ceramic parts. Gel injection molding is a suitable method for preparing a silicon carbide complex special-shaped piece, and utilizes silicon carbide ultrafine powder, boron carbide and carbon black to assist in firing, so as to obtain a ceramic product with high density.

At present, gel injection molding is carried out in a crosslinking and curing mode, so that a green body with high density can be obtained. However, moisture and dispersant are also locked in the crosslinked network along with the ceramic powder, and are difficult to be removed during drying, requiring a large amount of energy. Because the strength of the blank body is not large in the initial drying stage, larger internal stress can be generated under heating or pressure, and the blank body is cracked, layered and other defects. The problems of cracking of the green body and the like can be solved by properly increasing the proportion of the colloid, but at the same time, the cross-linked network structure is more compact, liquid such as water and the like is more difficult to remove, and the green body injection molded by pressureless sintered silicon carbide gel is difficult to dry, so the green body injection molded by pressureless sintered silicon carbide gel is required to be improved.

Disclosure of Invention

In order to improve the drying performance of a silicon carbide ceramic wet blank, the application provides a preparation method for pressureless sintering silicon carbide gel injection molding.

The preparation method of pressureless sintered silicon carbide gel injection molding provided by the application adopts the following technical scheme:

a preparation method of pressureless sintered silicon carbide gel injection molding is characterized in that: the method comprises the following steps:

Mixing and dispersing modified silicon carbide ultrafine powder, a monomer and a crosslinking agent into water, stirring, adding an initiator, carbon black and a dispersing agent, uniformly mixing, and then removing bubbles in vacuum to obtain mixed slurry;

adding the mixed slurry into a mold, immersing the bottom of the mold filled with the mixed slurry into a freezing bath, demolding after the reaction is completed to obtain a wet blank, drying the wet blank to obtain a dry blank, and performing pressureless sintering on the dry blank to obtain the silicon carbide ceramic.

The gel with the oriented micro-channel holes is synthesized by taking the oriented grown ice crystals as a template, when the bottom of the mould is slowly immersed in a freezing bath, the ice crystals start to grow unidirectionally from the immersed end to form a micro-channel hole structure, and the monomer originally dispersed in the slurry is concentrated in an amorphous area and is subjected to efficient polymerization under the action of an initiator, so that a finally obtained hydrogel sample has micro-scale channels which are arranged in parallel with the growth direction of the ice crystals, the removal of moisture in the drying process is facilitated, the problem of difficult drying is solved, and the stability of the silicon carbide ceramic is improved.

Preferably, the monomer is N-isopropylacrylamide.

N-isopropyl acrylamide is an acrylamide derivative monomer, has hydrophilic amide groups and hydrophobic isopropyl groups in molecules, has a lower critical dissolution temperature, and can quickly generate polymer gel under ice bath conditions.

Preferably, the mass fraction of the N-isopropyl acrylamide is 1-2% of the mixed slurry.

The wet blank prepared according to the mass fraction content has rich oriented micro-channel pore structure and is easy to dry.

Preferably, the crosslinking agent is N, N' -methylenebisacrylamide.

The N, N' -methylene bisacrylamide contains two allyl double bonds, can perform addition reaction with N-isopropyl acrylamide to form a cross-linked structure, and rapidly generates polymer gel.

Preferably, the mass ratio of the N-isopropyl acrylamide to the N, N' -methylene bisacrylamide is 1: (0.1-0.15).

The wet blank obtained according to the mass ratio has a pore structure with good appearance.

Preferably, the mass fraction of the carbon black is 0.8-1.2% of the mixed slurry.

Carbon black is a nanomaterial with high surface area and porosity, and can improve the density and hardness of silicon carbide ceramics, and the silicon carbide ceramics prepared according to the mass fraction content have high density and hardness.

Preferably, the silicon carbide ceramic further comprises boron carbide.

The boron carbide can greatly improve the hardness of the silicon carbide ceramic, so that the silicon carbide ceramic is more wear-resistant and corrosion-resistant; the boron carbide can improve the heat conductivity of the silicon carbide ceramic, reduce the heat loss of the silicon carbide ceramic at high temperature, and improve the quality and the service life of the silicon carbide ceramic.

Preferably, the mass fraction of the boron carbide is 0.5-0.7% of the mixed slurry.

The silicon carbide ceramic prepared according to the mass fraction content has high density and hardness.

Preferably, the initiator comprises an oxidizing agent, a reducing agent and a catalyst.

By constructing an initiation system, monomers and a cross-linking agent can be rapidly cross-linked and polymerized under the condition of a freezing bath to form polymer gel with a good pore structure, and the subsequent drying process is facilitated.

Preferably, the mass ratio of the oxidant to the reducing agent to the catalyst is 1:0.1: (0.2-0.3).

The wet blank prepared according to the mass ratio has good pore structure.

In summary, the present application includes at least one of the following beneficial technical effects:

1. The gel with the oriented micro-channel holes is synthesized by taking the oriented grown ice crystals as a template, when the bottom of the mould is slowly immersed in a freezing bath, the ice crystals start to grow unidirectionally from the immersed end to form a micro-channel hole structure, and the monomer originally dispersed in the slurry is concentrated in an amorphous area and is subjected to efficient polymerization under the action of an initiator, so that a finally obtained hydrogel sample has micro-scale channels which are arranged in parallel with the growth direction of the ice crystals, the removal of moisture in the drying process is facilitated, the problem of difficult drying is solved, and the stability of the silicon carbide ceramic is improved.

2. By controlling the dosage proportion of the monomer, the cross-linking agent and the initiator, the polymer gel with a good morphology structure is obtained, the water is discharged, and the drying performance and the stability of the silicon carbide ceramic are improved.

Drawings

FIG. 1 is a schematic view showing the whole body of the green body prepared in example 3 after drying in the preparation method of pressureless sintered silicon carbide gel injection molding according to the present application.

FIG. 2 is a schematic diagram showing the whole dried green body of example 3 in the method for preparing pressureless sintered silicon carbide gel according to the present application.

FIG. 3 is a schematic representation of the green body of example 12 in a method of preparing pressureless sintered silicon carbide gel injection molding according to the present application after drying.

FIG. 4 is a schematic representation of the green body of example 15 in a method of preparing pressureless sintered silicon carbide gel injection molding according to the present application after drying.

FIG. 5 is an internal schematic view of a green body prepared in example 15 of a method of preparing pressureless sintered silicon carbide gel injection molding according to the present application after drying.

FIG. 6 is a schematic diagram showing the whole body of the green body of comparative example 1 after drying in the method for preparing pressureless sintered silicon carbide gel injection molding according to the present application.

Detailed Description

The embodiment of the application discloses a preparation method of pressureless sintered silicon carbide gel injection molding, which is further described in detail by combining with the embodiment:

Examples

Example 1

Mixing and dispersing modified silicon carbide ultrafine powder, N-isopropyl acrylamide and N, N '-methylene bisacrylamide into deionized water, stirring for 30min at 200r/min, adding an initiator, carbon black, boron carbide and a dispersing agent, uniformly mixing, and removing bubbles in vacuum for 15min to obtain mixed slurry, wherein the modified silicon carbide ultrafine powder accounts for 50% of the mass of the mixed slurry, the N-isopropyl acrylamide accounts for 1%, the N, N' -methylene bisacrylamide accounts for 0.1%, the initiator accounts for 0.65%, the initiator comprises 0.5% of oxidant potassium persulfate, 0.05% of reducing agent ammonium bisulfate, 0.1% of catalyst palladium chloride, the carbon black accounts for 0.8%, the CE64 dispersing agent accounts for 1.2% and the boron carbide accounts for 0.5%. Adding the mixed slurry into a mold, immersing the bottom of the mold filled with the mixed slurry into a liquid nitrogen freezing bath for 15min, demolding after the reaction is completed to obtain a wet blank, drying the wet blank in a drying box, drying at 25 ℃ for 10h, heating to 35 ℃ for continuous drying for 10h, and finally heating to 45 ℃ for 3d to obtain a dry blank; and (3) placing the dried blank in a pressureless sintering furnace, and sintering for 3d at 1700 ℃ to obtain the silicon carbide ceramic.

Example 2

Mixing and dispersing modified silicon carbide ultrafine powder, N-isopropyl acrylamide and N, N '-methylene bisacrylamide into deionized water, stirring for 30min at 200r/min, adding an initiator, carbon black, boron carbide and a dispersing agent, uniformly mixing, and removing bubbles in vacuum for 15min to obtain mixed slurry, wherein the modified silicon carbide ultrafine powder accounts for 50% of the mass of the mixed slurry, the N-isopropyl acrylamide accounts for 2%, the N, N' -methylene bisacrylamide accounts for 0.3%, the initiator accounts for 0.7%, the initiator comprises 0.5% of oxidant potassium persulfate, the reducing agent ammonium bisulfate accounts for 0.05%, the catalyst palladium chloride accounts for 0.15%, the carbon black accounts for 1.2%, the CE64 dispersing agent accounts for 1.2% and the boron carbide accounts for 0.7%. Adding the mixed slurry into a mold, immersing the bottom of the mold filled with the mixed slurry into a liquid nitrogen freezing bath for 15min, demolding after the reaction is completed to obtain a wet blank, drying the wet blank in a drying box, drying at 25 ℃ for 10h, heating to 35 ℃ for continuous drying for 10h, and finally heating to 45 ℃ for 3d to obtain a dry blank; and (3) placing the dried blank in a pressureless sintering furnace, and sintering for 3d at 1700 ℃ to obtain the silicon carbide ceramic.

Example 3

Mixing and dispersing modified silicon carbide ultrafine powder, N-isopropyl acrylamide and N, N '-methylene bisacrylamide into deionized water, stirring for 30min at 200r/min, adding an initiator, carbon black, boron carbide and a dispersing agent, uniformly mixing, and removing bubbles in vacuum for 15min to obtain mixed slurry, wherein the modified silicon carbide ultrafine powder accounts for 50% of the mass of the mixed slurry, the N-isopropyl acrylamide accounts for 1.5%, the N, N' -methylene bisacrylamide accounts for 0.1875%, the initiator accounts for 0.675%, the initiator comprises 0.5% of oxidant potassium persulfate, the reducing agent ammonium bisulfate accounts for 0.05%, the catalyst palladium chloride accounts for 1%, the CE64 dispersing agent accounts for 1.2% and the boron carbide accounts for 0.6%. Adding the mixed slurry into a mold, immersing the bottom of the mold filled with the mixed slurry into a liquid nitrogen freezing bath for 15min, demolding after the reaction is completed to obtain a wet blank, drying the wet blank in a drying box, drying at 25 ℃ for 10h, heating to 35 ℃ for continuous drying for 10h, and finally heating to 45 ℃ for 3d to obtain a dry blank; and (3) placing the dried blank in a pressureless sintering furnace, and sintering for 3d at 1700 ℃ to obtain the silicon carbide ceramic.

Example 4

Example 4 based on example 3, example 4 differs from example 3 only in that the mass ratio of N-isopropylacrylamide in example 4 is 0.5% and the mass ratio of N, N' -methylenebisacrylamide is 0.0625%.

Example 5

Example 5 based on example 3, example 5 differs from example 3 only in that the mass ratio of N-isopropylacrylamide in example 5 is 2.5% and the mass ratio of N, N' -methylenebisacrylamide is 0.3125%.

Example 6

Example 6 based on example 3, example 6 differs from example 3 only in that the mass ratio of N-isopropylacrylamide in example 6 is 1.5% and the mass ratio of N, N' -methylenebisacrylamide is 0.075%.

Example 7

Example 7 based on example 3, example 7 differs from example 3 only in that the mass ratio of N-isopropylacrylamide in example 7 is 1.5% and the mass ratio of N, N' -methylenebisacrylamide is 0.3%.

Example 8

Example 8 based on example 3, example 8 differs from example 3 only in that the mass ratio of carbon black in example 8 is 0.6%.

Example 9

Example 9 based on example 3, example 9 differs from example 3 only in that the mass ratio of carbon black in example 9 is 1.4%.

Example 10

Example 10 based on example 3, example 10 differs from example 3 only in that the mass ratio of boron carbide in example 10 is 0.4%.

Example 11

Example 11 is based on example 3, the difference between example 11 and example 3 being only that the mass ratio of boron carbide in example 11 is 0.8%.

Example 12

Example 12 based on example 3, example 12 differs from example 3 only in that in example 12 the oxidant mass ratio was 0.54%, the reductant mass ratio was 0.054% and the catalyst usage ratio was 0.081%.

Example 13

Example 13 is based on example 3, the difference between example 13 and example 3 being only that in example 13 the oxidant mass ratio is 0.465%, the reductant mass ratio is 0.047% and the catalyst usage ratio is 0.163%.

Example 14

Example 14 is based on example 3, the difference between example 14 and example 3 being only that no carbon black is added in example 14.

Example 15

Example 15 is based on example 3, the difference between example 15 and example 3 being only that no boron carbide is added in example 15.

Comparative example 1

Comparative example 1 based on example 3, comparative example 1 differs from example 3 only in that comparative example 1 replaces the liquid nitrogen freezing bath with a 40 ℃ water bath.

Performance test

(1) Density testing: samples were prepared as 100mm by 200mm by 20mm cubic silicon carbide ceramic test pieces, density was calculated from volume and mass, each sample was tested three times, and the average value was taken after measurement, and the results are recorded in table 1.

(2) The method for testing the room temperature hardness of the fine ceramics of GB 16534-2009 is selected as a standard, a Vickers hardness tester is used for testing, the Vickers hardness of each sample is calculated, each sample is tested three times, the average value is obtained after the measurement, and the result is recorded in Table 1.

(3) Drying performance test: the wet green sheet was subjected to drying treatment, and the dried green sheet was observed and recorded, and the results are shown in table 1.

TABLE 1 Density and hardness measurements of silicon carbide ceramics

Detection result	Density (g/cm ³)	Hardness (GPa)	After drying, there is no cracking
				Example 1	3.15	25	No cracking
Example 2	3.15	26	No cracking
				Example 3	3.16	28	No cracking
Example 4	3.11	24	No cracking
				Example 5	3.12	22	No cracking
Example 6	3.12	24	No cracking
				Example 7	3.13	23	No cracking
Example 8	3.12	21	No cracking
				Example 9	3.13	22	No cracking
Example 10	3.12	20	No cracking
				Example 11	3.14	22	No cracking
Example 12	3.13	18	Deformation of
				Example 13	3.11	17	Deformation of
Example 14	3.13	16	Deformation of
				Example 15	3.12	15	Deformation of
Comparative example 1	3.01	11	Severe deformation

As can be seen from Table 1, the density of examples 1-3 is greater than 3.15g/cm ³, the hardness is greater than 25GPa, and the dried blank is free from cracking, so that the silicon carbide ceramic prepared by the application has high density and hardness, and has good drying performance and service performance.

As can be seen from Table 1, examples 4-7 differ from example 3 only in that: the dosages of N-isopropyl acrylamide and N, N' -methylene bisacrylamide are changed in examples 4-7, the density in examples 4-7 is less than 3.13g/cm ³, the hardness is less than 25GPa, the green body is free from cracking after drying, the density in example 3 is 3.23g/cm ³, the hardness is 25GPa, and the drying performance, the density and the hardness are reduced in examples 4-7 compared with example 3; this is because the amount of the monomer and the crosslinking agent is changed, which affects the micro-crosslinked structure of the polymer gel, the size and the number of the pore diameter are changed, the pore structure is deteriorated, the discharge of water during drying is affected, the density and the hardness of the ceramic are further affected, and the usability of the silicon carbide ceramic is deteriorated.

As can be seen from table 1, examples 8 and 9 differ from example 3 only in that: the mass ratio of the carbon black in the embodiment 8 is 0.6%, the mass ratio of the carbon black in the embodiment 9 is 1.4%, the density in the embodiment 8 and the embodiment 9 is less than 3.13g/cm ³, the hardness is less than 22GPa, the dried blank is free from cracking, and compared with the embodiment 3, the embodiment 8 and the embodiment 9 have reduced density and hardness; this is because the amount of carbon black used varies, and too little or too little carbon black affects the thermal stability and sintering properties of the silicon carbide ceramic, and the density and hardness of the silicon carbide ceramic are reduced.

As can be seen from table 1, examples 10 and 11 differ from example 3 only in that: the mass ratio of the boron carbide in the embodiment 10 is 0.4%, the mass ratio of the boron carbide in the embodiment 11 is 0.8%, the density in the embodiments 10 and 11 is less than 3.14g/cm ³, the hardness is less than 22GPa, the green body is free from cracking after drying, and compared with the embodiments 10 and 11 and the embodiment 3, the density and the hardness are reduced; the method is characterized in that the consumption of the boron carbide is changed, and excessive or too little boron carbide can influence the heat conductivity of the silicon carbide ceramic, so that the heat loss of the silicon carbide ceramic at high temperature is increased, the density and the hardness of the silicon carbide ceramic are reduced, and the quality and the service life of a product are reduced.

As can be seen from table 1, examples 12 and 13 differ from example 3 only in that: the mass ratio of the oxidant, the reducing agent and the catalyst in example 12 is 1:0.1:0.15, the mass ratio of the oxidant, the reducing agent and the catalyst in example 13 is 1:0.1:0.35, the density of the examples 12 and 13 is less than 3.13g/cm ³, the hardness is less than 18GPa, the blank body is deformed after drying, and the drying performance, the density and the hardness of the examples 12 and 13 are reduced compared with those of the examples 3; this is because the ratio of the components in the initiator is changed, and the change of the initiator system affects the polymerization speed of the monomer and the crosslinking agent, and further affects the pore structure of the polymer gel, so that the drying performance is affected, and the density and hardness of the silicon carbide ceramic are reduced.

As can be seen from table 1, examples 14 and 15 differ from example 3 only in that: carbon black is not added in example 14, boron carbide is not added in example 15, the density of examples 14 and 15 is less than 3.13g/cm ³, the hardness is less than 16GPa, the green body is deformed after drying, and the drying performance, the density and the hardness are all reduced compared with those of examples 14 and 15 and example 3; this is because the absence of carbon black or boron carbide, which is not added, affects the sintering properties of the silicon carbide ceramic, and the heat loss of the silicon carbide ceramic at high temperatures increases, and the density and hardness of the silicon carbide ceramic decreases, thereby reducing the quality and the service life of the ceramic.

As can be seen from table 1, comparative example 1 differs from example 3 only in that: in comparative example 1, the liquid nitrogen freezing bath is replaced by a water bath at 40 ℃, the density in comparative example 1 is 3.01g/cm ³, the hardness is 11GPa, the green body is seriously deformed after drying, and the drying performance, the density and the hardness are obviously reduced compared with those in comparative example 1 and example 3; the method is characterized in that the liquid nitrogen freezing bath is replaced by a water bath at 40 ℃, the polymerization speed of the monomer and the cross-linking agent is too high under the condition of high-temperature water bath, the guiding effect of an ice crystal template is lacked, and the pore structure of the polymer gel is disordered, so that the drying performance of a wet blank is affected, and the density and the hardness of the silicon carbide ceramic are obviously reduced.

The present embodiment is merely illustrative of the present application, and the present application is not limited thereto, and a worker can make various changes and modifications without departing from the scope of the technical idea of the present application. The technical scope of the present application is not limited to the contents of the specification, and must be determined according to the scope of claims.

Claims

1. A preparation method of pressureless sintered silicon carbide gel injection molding is characterized in that: the method comprises the following steps:

2. The method for preparing pressureless sintered silicon carbide gel injection molding according to claim 1, wherein the method comprises the steps of: the monomer is N-isopropyl acrylamide.

3. The method for preparing pressureless sintered silicon carbide gel injection molding according to claim 2, wherein: the mass fraction of the N-isopropyl acrylamide is 1-2% of the mixed slurry.

4. A method for preparing pressureless sintered silicon carbide gel injection molding according to claim 3, wherein: the cross-linking agent is N, N' -methylene bisacrylamide.

5. The method for preparing pressureless sintered silicon carbide gel injection molding according to claim 4, wherein the method comprises the steps of: the mass ratio of the N-isopropyl acrylamide to the N, N' -methylene bisacrylamide is 1: (0.1-0.15).

6. The method for preparing pressureless sintered silicon carbide gel injection molding according to claim 1, wherein the method comprises the steps of: the mass fraction of the carbon black is 0.8-1.2% of the mixed slurry.

7. The method for preparing pressureless sintered silicon carbide gel injection molding according to claim 1, wherein the method comprises the steps of: the silicon carbide ceramic also includes boron carbide.

8. The method for preparing pressureless sintered silicon carbide gel injection molding according to claim 7, wherein: the mass fraction of the boron carbide is 0.5-0.7% of the mixed slurry.

9. The method for preparing pressureless sintered silicon carbide gel injection molding according to claim 1, wherein the method comprises the steps of: the initiator includes an oxidizing agent, a reducing agent, and a catalyst.

10. The method for preparing pressureless sintered silicon carbide gel injection molding according to claim 9, wherein: the mass ratio of the oxidant to the reducer to the catalyst is 1:0.1: (0.2-0.3).